When the EchoServer starts up, it opens a server socket that listens for incoming connection requests. When it gets a request, it creates a new handler instance, taking the Socket as an argument. The handler is a Runnable class, and used to start a new Thread. The result is that the EchoServer can handle more than one connection at a time -- just like a good socket server should.

To expand on this, it would be a good idea to implement some means of managing the threads and connections. Using the java.util.concurrent API would be a good thing to do to implement some means of thread pooling in the server instead of using naked Threads. Thread pooling is an important thing to implement because each new persistent connection requires a new thread. Too many connections would cause some real resource problems. However, if there are limits to the amount of connections the server will allow, you need to manage connections. Therefore, some intelligence might need to be added to a Client program, so that a connection need only stay alive for a certain amount of time before becoming disconnected. Then, a well designed client might seamlessly create a new connection to the server.